Various information, e.g., music, speech and/or image, etc. have been permitted to be easily handled also by personal computer or mobile computer, etc. with digitization of data in recent years. Moreover, band-compression of these information has been realized by audio (speech) codec technology or image codec technology so that the environment where these information are easily and efficiently distributed (delivered) to various communication terminal equipments by digital communication or digital broadcast is being arranged. For example, audio/video data (AV data), etc. can be received at the indoor/outdoor by wireless system through mobile telephone, etc. without limitation only to reception by wire system
Meanwhile. with respect to the transmission/reception system for data, etc., suitable network systems have been constructed also within home and/or small area, and have been variously utilized. As the network system, attention is drawn to the various next generation wireless systems, e.g., narrow-band wireless communication system of 5 GHz band proposed in the IEEE802.11a, wireless LAN system of 2.45 GHz band proposed in the IEEE802.11b, and/or near distance wireless communication system called Bluetooth, etc. In the transmission/reception system for data, etc. such various wireless network systems are effectively utilized so that transmission/reception of various data, access to the Internet and/or transmission/reception of data can be made easily and without intervention of relay board, etc. at various places such as home or outdoors, etc.
In the wireless network systems, respective communication terminal equipments are permitted to be connected with respect to all communication systems so that effective utilization can be realized. Such wireless network systems not only lead to enlargement and/or high cost of communication terminal equipments, but also result in large burden also with respect to the communication infrastructure side. Communication terminal equipments are utilized not only at indoor but also at outdoor, etc., and are indispensable that they are compact and light in weight and are portable, and are inexpensive. For this reason, it is extremely difficult to constitute the communication terminal equipments so that they are adapted to the specification of such wireless network system.
In the communication terminal equipments, there is being made development of the so-called Software Defined Radio technology in which compliance is made by base-band processing below modulation/demodulation processing with respect to respective communication systems and/or frequency bands to thereby constitute wireless communication units as integral unit. However, even such SDR technology has vast calculation quantity for signal processing. As a result, even if compliance of burden at the communication infrastructure side can be realized, compliance of power consumption at the communication terminal equipment side and/or compliance of enlargement by integration are great problems. Particularly, it is difficult that portable communication terminal equipments are put to practical use.
A wireless communication module 100 shown in FIGS. 1 and 2 constitutes an analog front end of a wireless transmitter/receiver, wherein there is realized the so-called multi-band configuration in which base band portion is shared with respect to the same modulation/demodulation system or different modulation/demodulation system, and plural transmitting/receiving units are included (provided) to permit transmission/reception of wireless signals of different frequency bands. The wireless communication module 100 transmits or receives wireless signals of different frequency bands at an antenna unit 101.
The wireless communication module 100 comprises, as shown in FIG. 1, although the detail is omitted, a receive signal processing system 107 adapted for converting a high frequency signal received at the antenna unit 101 into an intermediate frequency signal on the basis of reference frequency delivered from a reference frequency generating circuit unit 103 at a RF-IF converting unit 102 to amplify the intermediate frequency signal thus obtained at an amplifier unit 104 thereafter to demodulate the intermediate frequency signal thus amplified at a demodulation unit 105 to output the signal thus obtained to base-band units 106. The wireless communication module 100 comprises, although the detail is omitted, a transmit signal processing system 110 for directly converting the intermediate frequency signal outputted from the base-band unit 106 into high frequency signal at an IF-RF converting unit 108 and demodulating that intermediate frequency signal to transmit the signal thus obtained from the antenna unit 101 through an amplifier unit 109.
Although the detail is omitted, the wireless communication module 100 is adapted so that large functional components (parts) such as various filters, Voltage Controlled Oscillator (VCO) and Surface Acoustic Wave (SAW) device, etc. are mounted between respective stages, and includes passive elements such as inductors, capacitors and/or resistors, etc. which are specific to high frequency analog circuit. At the wireless communication module 100, as shown in FIG. 1, first to third changeover switches 111 to 113 are provided at RF-IF converting unit 102, reference frequency generating circuit unit 103 or demodulation unit 105 of the receive signal processing system 107. Moreover, at the wireless communication module 100, fourth and five changeover switches 114 and 115 are provided also at IF-RF converting unit 108 or amplifier unit 109 within the transmit signal processing system 110.
Although the detail is omitted, the first to third changeover switches 111 to 113 are caused to undergo switching operation to perform capacity switching of variable capacitors and/or variable reactances to thereby perform control of time constant switching so as to match the frequency characteristic of receive signal. Although the detail is omitted, the fourth and five changeover switches 114 and 115 are also caused to undergo switching operation to thereby perform capacity switching of variable capacitors and/or variable reactances to perform control of time constant switching so as to match frequency characteristic of transmit signal.
The wireless communication module 100 comprises, as shown in FIG. 2, a module board (substrate) 120 comprised of multi-layered wiring board, and is constituted, although the detail is omitted, as the result of the fact that passive elements and/or capacity patterns, etc. constituting the above-described respective functional blocks are formed together with wiring patterns within respective wiring layers of the module board 120. At the module board 120, a high frequency signal processing LSI 121 and suitable chip components (parts) 122 are mounted on the surface thereof, and a shield cover 123 is assembled for the purpose of excluding the influence of electromagnetic noise. It is to be noted that, at the module board 120, antenna pattern constituting the antenna unit 101 may be formed at, e.g., a portion which is not covered by the shield cover 123 of the surface. In addition, at the module board 120, antenna unit 101 may be constituted by chip-type antenna mounted on the surface, or transmit/receive signal may be inputted or outputted from the antenna of separate member.
At the wireless communication module 100, as shown in FIG. 2, the above-described first to five changeover switches 111 to 115 are constituted by MEMS (Micro Electro Mechanical System) switches 130 mounted on the surface of the module board 120. As shown in FIG. 3, the entirety of the MEMS switch 130 is covered by an insulating cover 131. The MEMS switch 130 is mounted on module wiring board 120 as described above through leads 132 drawn from the insulating cover 131.
As shown in FIG. 3, the MEMS switch 130 is adapted so that a first fixed contact 134, a second fixed contact 135 and a third fixed contact 136 are formed on a silicon substrate 133, and a movable contact piece 137 in a thin plate form and having flexibility is fixed at the first fixed contact 134 and the free end thereof is cantilever-supported in a manner opposed to the third fixed contact 136. The MEMS switches 130 are respectively connected to leads 132 through wires 138 in the state where the first and third fixed contacts 134 and 136 are used as output contact. Additionally, the second fixed contact 136 is also connected to other lead 132. At the movable contact piece 137, an electrode 139 is provided at the portion opposite to the second fixed contact 135.
At the MEMS switch 130, as shown in FIG. 3, a silicon cover 140 is connected onto the silicon base 133 by, e.g., anode connecting method, etc. to allow the first to third fixed contacts 134 to 136 and the movable contact piece 137 to be maintained in the air-tight state. The entirety of the MEMS switch 130 is sealed by the insulating cover 131 so that the MEMS switch 130 is integrated as package. At the MEMS switch 130, as the result of the fact that the movable portion thereof is sealed by the silicon substrate 133 and the silicon cover 140 and the entirety thereof is sealed by the insulating cover 131, moisture resistance characteristic and oxidation resistance characteristic are maintained, and durability with respect to the mechanical load from the external is maintained.
At the MEMS switch 130 constituted as described above, when drive voltage is applied, the third fixed contact 136 and the movable contact piece 137 are shorted by electromagnetic attractive force produced between the second fixed contact 135 and the electrode 139 of the movable contact piece 137, and the short state thereof is maintained. At the MEMS switch 130, when reverse bias drive voltage is applied, the movable contact piece 137 is returned to the initial state by electromagnetic repulsive force produced between the second fixed contact 135 and the electrode 139 so that the short state with respect to the third fixed contact 136 is released. Since the MEMS switch 130 is a switch element which is extremely very small and does not require holding current for holding the operating state, it is possible to suppress enlargement of the wireless communication module 100 and to realize low power consumption.
The wireless communication module 100 as described above is caused to be of the configuration in which switching of time constant is performed by the MEMS switches 130 to thereby switch the frequency characteristics of the antenna, respective filters and/or VCO, etc. so that there results tunable state. Meanwhile, since the MEMS switch 130 has movable portion, first to third fixed contacts 134 to 136 and/or wiring patterns are finely formed on the silicon substrate 133 as described above, and the silicon base 133 and the silicon cover 140 are connected by the anode connecting method, etc. thereafter to cover it by the insulating cover 131 so that the MEMS switch 130 is caused to be of package configuration. Thus, MEMS switches 130 are mounted on the module board similarly to other mounting components (parts).
In the above-described conventional wireless communication module 100, there is the problem that the characteristic is lowered by the influence on the high frequency circuit unit resulting from reflection or loss from parasitic component of the MEMS switch 130. In the wireless communication module 100, there is the problem that MEMS switches are mounted on the surface of the module board 120 so that path lengths between the MEMS switches 130 and internal circuits are elongated, whereby the characteristic is lowered by the influence of the interference or loss. Further, in the wireless communication module 100, since the MEMS switch 130 has the structure that respective components are assembled on the silicon substrate 133 and are sealed by the insulating cover 131 so that they are packaged, further miniaturization is difficult.
In the above-described conventional wireless communication module 100, e.g., SAW device (Surface Acoustic Wave Device), and/or IC and LSI for micro-wave or mili-wave, etc. are also mounted. There is the problem that in the case where these elements are coated by insulating resin, their characteristics are remarkably deteriorated.